The invention relates to a circuit for maintaining constant sliver density and thickness in a card or the like.
One step in the processing of textile fibers, such as cotton, wool, synthetic fibers or any type of textile fibers is forming these small fibers into a long inter-lock chain known in the art as a sliver. This function is usually accomplished by a machine termed a card, but other textile processing equipment such as draw-frames and pin drafters also produce slivers. These slivers are conventionally coiled or otherwise stored for further processing into textile yarn or thread, which can then be woven or otherwise manipulated into textile material. It is important that the density or thickness of the sliver be maintained substantially uniform. In the absence of monitoring of this thickness or density, the sliver density has a tendency to drift away from a desired value, thus producing a product which is unsatisfactory for further processing. In view of the speed of operation of modern carding machines, it is virtually impossible for visual observation or periodic manual testing to satisfactorily maintain a desired density.
Thickness regulating devices commonly known by the term "autolevelers" are well-known in the textile art and have been successfully employed for many years. For example, Crossroll manufactures an autoleveler in which the relative positions of two rollers between which the sliver moves are detected to produce an electrical signal, which is integrated and compared electrically with a desired value to control the relative speeds of the doffer and feed rolls of the card machine. U.S. Pat. No. 3,938,223 describes an apparatus in which the thickness and density of a sliver passing between a rotating grooved roller and a sensor roller is detected by movement of a magnetic core to vary the coupling between primary and secondary windings of a transformer. Preferably the transformer includes first and secondary coils so that the amplitudes of the respective output voltages of these coils are directly related to the position of the core and, accordingly, the thickness of the sliver. The signals produced by the two secondary coils are delayed in time by a simple integration circuit to avoid changes in density resulting from detecting a minor irregularity in the sliver and applied to a first differential amplifier which produces an output voltage, which output voltage varies as a function of the difference between the two input signals.
The output voltage is in turn applied to a second differential amplifier which is periodically rendered operative by a pulse generator for a short period. The other input to the second amplifier is used to adjust the desired sliver thickness. When the second amplifier is activated, an amplified signal is applied to a pair of relays, one responsive to positive excursions of the wave form and the other responsive to negative excursions. Each of these relays operates a control switch which when the relays are activated completes a current path through a coil of a conventional control device which operates an armature to control a variable speed device connected to one of the two rollers which control the thickness of the sliver, for example, the feed roll of a conventional card.
In co-pending application Ser. No. 792,765 filed May 2, 1977, entitled AUTO-LEVELER an apparatus is described which is particularly useful for producing an electrical output signal which varies as a function of sliver thickness. As the sliver passes through a bore in a trumpet, the thickness is pneumatically sensed and a magnetic core shifted vertically in position with respect to a driven and a driving coil to produce an output signal. The disclosure of this co-pending application is hereby incorporated into the present application
The present invention relates to a circuit which finds particular utility with an auto-leveler of the type described in the above-mentioned co-pending application. The circuit of the present invention produces particularly accurate and reliable control of the feed motor of a card or the like. Signals indicating the respective speeds of the doff and feed rollers are produced as positive and negative DC voltages respectively which are applied to the opposite ends of a resistor. A signal from a sensor indicating the sliver thickness is then added to the signal representing the difference in speed between the doff and speed rolls. That signal is in turn added to a signal representing the torque of the feed motor to produce a control signal which is then compared with a ramp signal to control the speed of the feed roller.
Other objects and purposes of the invention will become clear from the following detailed description of the drawings.